5F4 issue...

[SleepLess]

There you go: you'll also notice a high-pitched noise at one point (about when I show the ground buss bar)...

 http://youtu.be/UJcfSiKNZ8A

Thanks!

[sluckey]

I think that is normal behavior. How does the amp sound musically?

[SleepLess]

I think that is normal behavior. How does the amp sound musically?

Oh my... really??? What about that squeal at 0:51 which sounds like a high-pitched beep???
I tapped the Bright channel input 1 only because it's the only one that pops, the other three are quiet when I do the same test...

I get the same kind of pop when I switch ON/OFF the pedals... Which indicates it's not the pedals, right?
Why is this freakin' jack popping like this while the others are silent?

The amp sounds good, but it is too noisy I think and I can't use any pedals with it...

I know I'm a newbee compared to you sluckey and to you HotBlue, but I have built about twenty-five amps including 12 tweeds (Champ, Super, 5E3, 5F6A) and it's the ONLY one that is this noisy and that has these pops at the input jack...

[SleepLess]

OK, so how's it sounds (no pedals, just straight into the amp!)

Fender Tweed Super 5F4 Replica

[sluckey]

I did hear the single beep at 51 seconds, but it was so short that I just dismissed it.

As for the background noise, that sounds like what I'd expect to hear with an amp set on 10 of 12 with fluorescent lighting. If you have any fluorescent lights on in that room, turn them off and see if the background noise decreases.

And the chopstick tapping on the bright #1 jack tip should produce a pop when you tap hard enough to open the switch contact. If you plug your guitar into the bright #1 jack, I don't expect tapping on that jack would cause any pops. But if you now tap on the emply normal #1 jack, I would expect popping.

Try this. Turn the amp off with nothing plugged into any of the input jacks. Connect one lead of your ohm meter to chassis. Connect the other lead to V1-7. What resistance do you measure? Now, with the meter still connected to V1-7, plug a cable (no guitar) into the bright #1 jack. What resistance do you measure?

The only suspects I have at this point would be a missing/faulty 1meg resistor on the #1 jack, bad wire between the jack and board, bad wire between board ond V1-7, bad/dirty V1 socket, or bad V1 tube.

BTW, I'm not an expert. I'm just a hobbyist. I've only had my hands on 13 amps in the last 30 years.

Do the resistance measurments and give us the numbers.

[SleepLess]

Try this. Turn the amp off with nothing plugged into any of the input jacks. Connect one lead of your ohm meter to chassis. Connect the other lead to V1-7. What resistance do you measure? Now, with the meter still connected to V1-7, plug a cable (no guitar) into the bright #1 jack. What resistance do you measure?

Done. MM set on 200K range:
No cable plugged in: 34.7K
Cable plugged in Bright 1: 37.5K

BTW, I'm not an expert. I'm just a hobbyist. I've only had my hands on 13 amps in the last 30 years.

Do the resistance measurments and give us the numbers.

If you're not an expert you're pretty darn close to one to me! You have saved me in several occasions and you always know what to do and check. I am about three decades in amp knowledge behind you. And I'm still billion of years behind thinking about creating my own amp with my own schematic...

[sluckey]

No cable plugged in: 34.7K
Cable plugged in Bright 1: 37.5K

The reading with no cable is good, but the reading with cable plugged into Bright 1 is bad. It should be 1meg ohm.

Please check again.

And also repeat the test for the normal channel, but checking V1-2 and plugging into normal #1 jack.

BTW, nice playing. I noticed you also had the volume turned up on the normal channel. I would keep the unused channel volume on zero to minimize noise. Or, I'd jumper the channels.

[SleepLess]

Thanks sluckey.

NORMAL channel (MM ground/pin2 of V1)
NO cable: 34.4K Ω
With cable in Input 1: 37.1K Ω

BRIGHT channel (MM ground/Pin7 of V1)
NO cable: 34.7K Ω
With cable in Input 1: 37.5K Ω

So I confirm my first readings... I do get 37.K with the cable in... That's a long way from 1M Ω!!!

Oh and I have changed my 1M resistor on the Bright channel twice already, so unless I'm really unlucky and I used three bad 1M Ω resistors... (and they test 1M Ω when I measure them once they're out of the circuit!)

[sluckey]

So I confirm my first readings... I do get 37.K with the cable in... That's a long way from 1M Ω!!!

You don't have a guitar connected to that cable, right?

I don't suspect the 1meg resistor, but the jacks cannot be wired correctly.

[SleepLess]

So I confirm my first readings... I do get 37.K with the cable in... That's a long way from 1M Ω!!!

You don't have a guitar connected to that cable, right?

I don't suspect the 1meg resistor, but the jacks cannot be wired correctly.

Oh my... I had the guitar at the other end of the cable  ... So here are the readings without the guitar:

NORMAL:
NO cable: 34.4KΩ
With cable: 1.17MΩ

BRIGHT:
NO cable: 34.8KΩ
With cable: 1.12MΩ

Sorry sluckey...

[sluckey]

That's more like it. All readings look good. Try another tube in the V1 socket. 12AX7 will work if you don't have another 12AY7. Plug/unplug several times to wipe the socket pins clean. Use some contact cleaner if you have it. DON'T USE WD40!

I still believe that tapping on that empty Bright #1 jack with a chopstick while the amp volume is set on 10 should produce a loud pop sound. Maybe some of the experienced guys that do this professionally will ring in with their opinions.

[SleepLess]

That's more like it. All readings look good. Try another tube in the V1 socket. 12AX7 will work if you don't have another 12AY7. Plug/unplug several times to wipe the socket pins clean. Use some contact cleaner if you have it. DON'T USE WD40!

I still believe that tapping on that empty Bright #1 jack with a chopstick while the amp volume is set on 10 should produce a loud pop sound. Maybe some of the experienced guys that do this professionally will ring in with their opinions.

Yep. So I have changed V1 (have some spare 12AY7s that I know work well) and nothing got better. I noticed that V2 pin 2 is a little bit noisy when I touch it with my chopstick. The rest of the amp is silent, save for that stupid hiss and those high-pitched squeals/interferences that occur from time to time (as heard in the second video at 0:51).

Next thing was to do my pedalboard test and the results are as bad as when I got the amp. Whatever input I plug the guitar in I get some really loud pops when I switch ON/OFF the pedals. Of course they're barely hearable with the guitar in either inputs 2, but they're huge in inputs 1. I know about the static discharge thing but this can't be IT because the pop remains as loud as it is on the first switching ON or the twentieth (yes, I tried 20 times to see if the pop volume would decrease!).

What a frikkin' amp... Can't debug this one... Crap. I think that I'm gonna try another 9 pins socket in V1 and see if I still get those sounds. Maybe it's just a dirty or bad V1 socket (or V2?).

I'll shoot another video tomorrow morning to show you the pedals pop. You'll see they're not normal. I mean, you could hear these pops during a concert with the amp on 9... That's totally unbearable...

[SleepLess]

There you go:

http://youtu.be/0talvPolcIc

If you have any suggestions, please feel free. I can't return the amp the way it behaves with pedals (notwithstanding the extraterraneous noise that comes from time to time...)
I plugged the guitar in Bright 1 but the pops are the same in Normal 1. It's just not as loud in inputs 2 but I guess that's normal. The 1MΩ resistor on inputs 1 seem toi boost those damn pops...
Thanks.

[sluckey]

OK, I agree. That's not right. My gut tells me the problem is with the input jacks and/or V1. But since the pops occur on either channel the problem should be something common to both channels. Get a good set of voltage readings for the amp. And don't omit zero volt readings. They're important too.

Did you just build this amp? Has it ever worked right? Is this a customer's amp? What's the story?

[SleepLess]

OK, I agree. That's not right. My gut tells me the problem is with the input jacks and/or V1. But since the pops occur on either channel the problem should be something common to both channels. Get a good set of voltage readings for the amp. And don't omit zero volt readings. They're important too.

Thanks sluckey. I know it's not right, I have built about ten tweeds including another 5F4 and it's the only one that does this. But I must admit, I had a hard time convincing you this one has something wrong...  

Here's the voltage chart. I went for the most accurate readings possible. B+ is 390V and tubes are 6L6 (30w max dissipation). 70% of that max dissipation gives 21w. So I did 21/390 which gives 56mA. Tubes are biased 10mA below that at 46mA. I can't go above, I'm already up full on the bias pot (33K resistor soldered across it) and my B+ is already quite low I think since the original fender schematic shows a 410V B+... When I say (200mV) it means that the readings were taken with the MM set on the 200mV range.

              Tube
Pin            V1                   V2                 V3                  V4                   V5                  V6          
1             134                  176               194.9         00.2(200mV)             0                   125.2(200mV)      
2           00.8(200mV)     5.6(200mV)       8.1(200mV)      3.38AC             3.38AC              405        
3             2.1                  1.25              1.53                388                  387                  00.5(200mV)      
4            3.38AC            3.38AC            3.38AC             393                  393                 350AC                                                
5            3.38AC            3.38AC            3.38AC            -34.3               -34.5                 0                                              
6            130.4                270               260                -34.4               -34.5                350AC    
7           3.3(200mV)         176               22.2               3.38AC             3.38AC              0    
8             2.1                  177.3             70.2               00.2(200mV)         0                  406        
9           3.38AC             3.38AC            3.38AC

Did you just build this amp? Has it ever worked right? Is this a customer's amp? What's the story?

Yes, I built this amp back in April. It worked well. I don't remember trying it with pedals though, but I think I did and obviously it didn't pop or I wouldn't have sent it. Its owner lives 400 miles away from me so I shipped it over to him and it worked well. Then I think about two months later he had to change the power tubes (NOS 5881s) because one of them failed. He also stated that the amp was making noise (probably the same kind of noise it makes today) and that pedals popped. He also told me that he inserted a preamp tube the wrong way and lit the amp with it...
That's when I told him to stop doing anything to it and to take it to a local tech. He did and the amp was actually returned to him with more noise and more pedal pops than before, which is when I asked him to return it to me...
He doesn't remember which preamp tube he mis-inserted...
I don't know more than this...

[SleepLess]

I've just had an email from its owner. He said the amp worked well upon arrival up until June (I shipped it in April). Then in June the pedals started popping. That's when he misinserted the power tubes and then took it to his tech.

I need your help.
Thanks.

[sluckey]

OK, here's what I suggest. We have to eliminate the input jacks/wiring. So, totally remove all 4 input jacks. And unsolder the two white wires on V1 socket, pins 2 and 7. Now install a single input jack. Use shielded cable and connect the jack directly to V1 as shown. Don't forget the jumper between pins 2 and 7.

Does this solve the popping? This is just a test but leave it like this until the popping is fixed.

[SleepLess]

Done.
Doesn't solve the popping...

[sluckey]

OK, now we know it's not the jacks. That's progress. Next, replace the onboard 820Ω and 25µF cap that's connected to V1 pins 3 and 8. Does that fix it?

If not, replace V1 tube socket. Fixed now?

[SleepLess]

OK, now we know it's not the jacks. That's progress. Next, replace the onboard 820Ω and 25µF cap that's connected to V1 pins 3 and 8. Does that fix it?

Nope... Pops remain...

If not, replace V1 tube socket. Fixed now?

Good Lord... Nope, they're still here... Looks like V1 is not the problem... 

[Willabe]

I wonder if the eyelet board has gone bad? Fenderitis?

Doug has brought this up before as have others.

Did the client live in a high humidity area?


                  Brad      

[SleepLess]

I wonder if the eyelet board has gone bad? Fenderitis?

Doug has brought this up before as have others.

Did the client live in a high humidity area?


                  Brad      

No, common average humidity...

[sluckey]

Describe your grounding system, especially concerning the board, power transformer high voltage center tap, and filter caps. Pics will help.

I still think its a bad connection. May not be a solder joint. May be a mechanical connection to the chassis. Could even be a component lead that is fractured inside a resistor or cap. Keep banging the chopstick.

[SleepLess]

- Power cord grounded to a PT screw, by itself.
- Other PT screw is the ground for the HT CT and the stdby switch cap.
- 6L6s are grounded to a single ground point which is one of V5's screws.
- All the rest (HV CT through the first filter cap, board grounds, input jacks) go to the floating buss bar which is itself grounded to the side of the chassis, near the input jacks.

The pics:









Now I'm off for some more banging... Jeez this amp is the hardest debug I've had yet to do... I have already spent more time debugging it (and to no avail!) than building it! Crazy!

[SleepLess]

I have just finished a 20-minute chopstick banging session (sounds cool huh?). I have changed a couple of resistors (the 270KΩ) and one 100KΩ that connects to V1 pin 1 because they were making some noise when tapping on them. But the pedals still pop even with the new ones.

I turned the amp full up, everything on 12, while doing this. This amp is sick let me tell you. It's like wind blowing through the speakers, but wind with some trees cracking in the distance. Definitely not healthy.

But nothing makes noise when tapping on the components, and I banged for 20 minutes... The customer says it worked flawlessly for two months, then his pedals started popping... 
I'm stumped...

No one wrote about my latest voltage chart, so I guess everything is fine...?

[SleepLess]

Hi.

I thought I had made significant progress with this test but apparently not:
- I pulled V3 out and lit the amp up, everything on 9. No pedals pop!!!!!
But then I put V3 back in and pulled V2, and then V2 back in and pulled V1, and no pops either...

The only thing I know is that whatever preamp tube I pull out, the pedals stop popping. Is this significant? Whan can it mean? Does it point to a certain area in the amp?
Thanks!

[sluckey]

Pulling any little tube will break the signal path, killing any sound from the amp, including pops. That's normal.

Your tube voltages did not reveal anything to me.

You seem to have two 100Ω resistors connected as an artificial center tap for the filaments but you also have the PT filament center tap lead grounded. Use one or the other but not both. I suggest removing the 100Ω resistors.

Your ground scheme needs to be totally redone. Study the grounding scheme at this link then make yours look like it.
http://www.el34world.com/charts/grounds.htm

More on grounding... Your power cord ground is fine. Basically you want both PT centertaps, power tube cathodes, first and second filter caps, and bias cap ALL CONNECTED TOGETHER NEAR THE PT. It's fine to use a PT bolt but use a star washer or kep nut. Use at least an AWG18 size buss wire.

There are many successful grounding schemes out there. Mine differs slightly from Doug's, but Doug's scheme is very good. Rather than add confusion, just go by his scheme. I know it's a lot of work, but it needs to be done. And it will probably cure this amp. I still believe there's a bad connection involved, but hopefully it will get fixed during your ground overhaul.

[SleepLess]

Pulling any little tube will break the signal path, killing any sound from the amp, including pops. That's normal.

OK. I should have guessed that...

Your tube voltages did not reveal anything to me.

Fine. At least it means that everything works properly...

You seem to have two 100Ω resistors connected as an artificial center tap for the filaments but you also have the PT filament center tap lead grounded. Use one or the other but not both. I suggest removing the 100Ω resistors.

OMG. How could I skip that all that time?  I have removed the 100Ω resistors from the lamp and ground. Only the HT CT remains grounded, but that didn't solve anything... The amp actually seems to be even noisier without the 100Ω resistors...

Your ground scheme needs to be totally redone. Study the grounding scheme at this link then make yours look like it.
http://www.el34world.com/charts/grounds.htm

More on grounding... Your power cord ground is fine. Basically you want both PT centertaps, power tube cathodes, first and second filter caps, and bias cap ALL CONNECTED TOGETHER NEAR THE PT. It's fine to use a PT bolt but use a star washer or kep nut. Use at least an AWG18 size buss wire.

There are many successful grounding schemes out there. Mine differs slightly from Doug's, but Doug's scheme is very good. Rather than add confusion, just go by his scheme. I know it's a lot of work, but it needs to be done. And it will probably cure this amp. I still believe there's a bad connection involved, but hopefully it will get fixed during your ground overhaul.

OK, I'm almost done with that... But one more thing before I continue:
I have a bias mod done in that amp:
- 56KΩ resistor removed from the board (but the ground wire between the 100uF/100V cap and the missing 56KΩ remains)
- The 6.8KΩ resistor has been removed and replaced by a 2w 470Ω.
- Bias pot is a 10KL with a 33KΩ resistor across it. The right lug receives the diode, the middle lug receives a cable that goes to the board where the other leg of the diode should have gone.
Is anything wrong with that?



Thanks!

[sluckey]

I want to see a pic that clearly shows every component in the bias circuit.

[SleepLess]

I want to see a pic that clearly shows every component in the bias circuit.

Tell me if you need more Steve. I just followed Marsh Amps' 5F4 Bias Mod. I didn't invent anything. But if their mod contains a flaw, then I implemented that flaw for sure...

[sluckey]

Bias mod is OK. I just needed to see it (especially the diode) to understand what you were describing.

[SleepLess]

Bias mod is OK. I just needed to see it (especially the diode) to understand what you were describing.

That's a good thing.
I have redone the grounding as per your instructions except for one thing: I left the floating ground buss bar and used it for the pots, input jacks and caps #3, #4 and #5. The rest is:

PT bolt: - power ground cord.
Other PT bolt: - HV CT + Bias cap and 1st Filter Cap + 6L6s cathodes + Stdby switch Cap.

Needless to say it hasn't changed a damn thing...
I'm about to send back this damn amp the way it is... It frikkin' upsets me.

[sluckey]

I left the floating ground buss bar and used it for the pots, input jacks and caps #3, #4 and #5.

I was hoping you would rip that buss out completely and totally redo it. Doing so may reveal/cure a bad connection.

Let's get in sync on the cap numbers... Starting with the left end of the board on the layout, call the bias cap #1, the next cap (plate) is #2, the next cap (screens) is #3, the next cap (PI) is #4, and finally, the next cap (preamp) is #5. My point is that caps 1, 2, and 3 need to connect directly to the power ground. Take cap 3 (screens) off the buss. This will involve moving an underboard jumper (sorry).

I feel your frustration with this amp, but I know it's fixable. At this point, if it were my personal amp I'd probably pull the board and start all over. Of course, doing so, you may never know what the exact problem is, if that's important. I hate working inside a narrow tweed chassis.

[worth]

Relfow all heater wire connections at the tubes, lamp , etc. It sounds like a weak heater joint.If you've done it already.. do it again.

[SleepLess]

Relfow all heater wire connections at the tubes, lamp , etc. It sounds like a weak heater joint.If you've done it already.. do it again.

I will do this again, before removing the board (a second time...). I had the buss bar across the pots first but I figured I'd use a floating buss bar instead as I don't much like soldering across pots: first they can get damaged with the iron's heat and second if they get too noisy and need to be replaced one day it's a lot easier to remove them and replace them if the bar is not running across them...

Anyway, sluckey I didn't remove cap #3 from the buss bar because the link you provided has it grounded to the buss bar... Only #1 and #2 go to the PT bolt. But if you say #3 has to go to the PT bolt as well, then I will remove that board again...

I'll never thank you all enough! I would have sent it back and told the guy "well just don't play it with pedals dude!" if you hadn't been here... 

[sluckey]

I didn't remove cap #3 from the buss bar because the link you provided has it grounded to the buss bar... Only #1 and #2 go to the PT bolt.

Don't confuse the cap #s for your specific board with the cap #s of Doug's generic drawing. Doug's #1 cap is really your #2 cap and his #2 cap is really your #3 cap. Doug's filter caps aren't even on the board in his drawing.

I don't like the buss bar attached to the pots either. That's one minor difference between the method I use versus Doug's method.

[SleepLess]

I didn't remove cap #3 from the buss bar because the link you provided has it grounded to the buss bar... Only #1 and #2 go to the PT bolt.

Don't confuse the cap #s for your specific board with the cap #s of Doug's generic drawing. Doug's #1 cap is really your #2 cap and his #2 cap is really your #3 cap. Doug's filter caps aren't even on the board in his drawing.

I don't like the buss bar attached to the pots either. That's one minor difference between the method I use versus Doug's method.

OK, I was going to make a mistake... So basically:
- 100uF/100V cap is my #1
- First 16uF/475V cap is my #2
- Second 16uF/475V cap is my #3
And all these three caps need to go to the same PT bolt along with all the CTs (HV + HT), the cathodes ground and the stdby switch cap?

If so, can I link caps #2 and #3 and use one wire to ground them or do they need to meet only at the PT bolt?

Sluckey can I keep my floating buss bar with only the right stuff attached to it or do you advise that I get rid of it and reinstall it directly on the pots?
Thanks!

[sluckey]

Remove the underboard jumper between #3 and #4. Jumper #1, #2, and #3 together on the board  and use a single #18 stranded wire to connect all to the same bolt with the PT center taps and power tube cathodes.

This is a good thing to do but it's not likely to fix your problem.

[SleepLess]

Heater wiring reflowed... Pedals still pop... I'm on my way to remove the board once again...

Hold on hold on... I have just had a long look at my heater wiring... The heaters between V4 and V3 are reversed... That may be the cause of the pops... V4 pin 2 goes to V3 pin 9 instead of going to pins 4/5 and V4 in 7 goes to V3 pins 4/5 instead of pin 9... I'll try this first before removing the board...

If this is it I'm the biggest fool on the planet... 

[SleepLess]

It wasn't that either... Pedals still pop... 

I'm off to take the board out.

[punkykatt]

I could be all wet, but those pedal pops sound like there is DC voltage on the signal.  Two years back I built a XLR mic switcher and if we used phantom powered mics it made a loud pop just like your pedals are doing??? To rule that out, plug  a guitar cable into the amp and measure  between the tip and sleeve of the other end for DC voltage.
Punky

[SleepLess]

OK. Three more hours on this. I took out the board and reflowed some joints, checked my wiring for the fourth time, chose the grounding scheme as per what you said sluckey: Caps #1, #2 and #3 now go to the PT bolt. The rest of the board goes to the buss bar.

And guess what... Pedals still pop, and the amp is even noisier now than it was before.

punkykatt thanks for your help. I turned the amp on with a guitar cord in Bright Channel Input 1 and I have 89.5mV (MM on 200mV range) at the other end of the cable (MM black lead to sleeve, red lead to tip). Would that be enough voltage to cuase the pops? I don't know...

Thanks.

[punkykatt]

Try disconnecting the cap to ground on the standby switch. See if that does anything for the pops.

[sluckey]

Is the chassis aluminum or steel? Is there any kind of coating or plating on the chassis that may need to be scraped off at every ground connection?

Oh, and I know this is a stretch, but disconnect the NFB wire from the speaker jack.

[SleepLess]

Try disconnecting the cap to ground on the standby switch. See if that does anything for the pops.

I will to this tomorrow morning. I have put it aside for tonight, I have some unexpected friends at home...

Is the chassis aluminum or steel? Is there any kind of coating or plating on the chassis that may need to be scraped off at every ground connection?

Oh, and I know this is a stretch, but disconnect the NFB wire from the speaker jack.

I will sluckey. The chassis is from Mojotone. I have built about ten tweeds using their chassis. I never had anything to scrape off on those...

[SleepLess]

Try disconnecting the cap to ground on the standby switch. See if that does anything for the pops.

It didn't do anything for the pops...

Oh, and I know this is a stretch, but disconnect the NFB wire from the speaker jack.

It didn't do anything either, it just added some low frequency hum... Pedals still pop.

Could these pops be the consequence of a bad OT or PT, or choke maybe? I mean, I have tested every single resistance, changed some, the voltages on the sockets are good. I have almost changed every coupling cap. This amp screams "I'm fine" but it's not... What the hell...

[SleepLess]

What if it was the 5U4GB I have?

I don't have any direct replacement, all I have is a 5Y3GT and a 5AR4 and possibly a GZ34 (it's not labeled but I think it's a GZ34). Which one can I use as a short replacement just to see if the one I have is any good?

Thanks!

[sluckey]

I don't suspect the 5U4, but I'm about out of ideas, so try it. The 5AR4 (same as GZ34) will work fine. That 5Y3 is too little.

I also don't suspect the transformers.

[SleepLess]

I don't suspect the 5U4, but I'm about out of ideas, so try it. The 5AR4 (same as GZ34) will work fine. That 5Y3 is too little.

I also don't suspect the transformers.

Right, I confirm that it's not the 5U4. I get the same pops with the 5AR4...

Jeez... If you're running out of ideas then I'm lost... 

[SleepLess]

I'm taking the 5F4 tonight for rehearsal. I have a three-hour rehearsal planned. I'm gonna push this little beast and hope it will explode. If it does then at least I'll know what to change... 

And if it doesn't then it's going back to its owner on Thursday...